(a) Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to an apparatus and method of acquiring initial synchronization of a terminal in a mobile communication system.
(b) Description of the Related Art
In general, a terminal in a mobile communication system needs to acquire synchronization first in order to perform communication between the terminal and a base station. When the terminal does not acquire the synchronization first, if a signal is transmitted or received, the received or transmitted signal serves only as an interference signal or noise between the terminal and the base station and does not allow any kind of information to be obtained. Therefore, it is a very important factor to acquire the initial synchronization between the terminal and the base station in all mobile communication systems.
Among the above mobile communication systems, a mobile communication system that uses code division multiple access (CDMA) has been widely used. However, the transmission of a larger amount of data in the CDMA mobile communication system is limited due to a bandwidth and a drain of resources.
A mobile communication system that uses orthogonal frequency division multiple access (hereinafter, for better comprehension and ease of description, referred to as “OFDMA”) is provided as one of the methods to solve the above-described limit. The OFDMA is one of the multi-carrier modulation methods and shows excellent performance in a multi-path mobile reception environment. Therefore, research and development have been actively made in the field of broadcasting.
However, as described above, a terminal in the OFDMA mobile communication system that has the characteristics needs to acquire initial synchronization first in order to exchange data with a base station. A process of acquiring initial synchronization of the terminal will now be described.
First, in order to acquire initial synchronization, the terminal receives a signal from the base station. The signal includes a preamble and a data field. An example of this is shown in FIG. 1.
As shown in FIG. 1, a downlink frame 100 that is a signal received from the base station includes a preamble signal 110 and a data field 120 that has a pilot signal.
The terminal acquires initial synchronization using an auto-correlation characteristic of the preamble signal 110 of the received downlink frame. At this time, due to a periodical pilot pattern of the data field 120, the auto-correlation characteristic is greatly generated even at a position where the pilot signal is allocated.
That is, when the pilot pattern of the data field 120 is repeated by a number corresponding to a multiple of a number by which a pattern is repeated in a time domain of the preamble, the auto-correlation characteristic with respect to the pilot signal is greatly generated. As a result, when acquiring the initial synchronization, the terminal cannot search an accurate symbol start point due to an auto-correlation characteristic of another signal, not the preamble signal. This leads to an increase in false alarm rates.
Further, the wrong symbol start point that is searched by the terminal generates inter-symbol interference. Therefore, the signal received from the base station cannot be recovered properly.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.